1. Field of the Invention
The present invention relates to a liquid crystal display process, and more particularly, to a method of forming a thin film transistor on a transparent plate.
2. Description of the Related Art
Active matrix LCDs (Liquid Crystal Displays) have been developed for mass production. The active matrix LCDs are highly integrated circuits whose level of integration is enhanced by using a technique of producing a semiconductor film on a substrate. The active matrix LCDs enable display of animation with high resolution. Such high resolution animation is obtained with a TFT (Thin Film Transistor), which is a switching element of a matrix display portion, disposed on one of two substrates with a liquid crystal interposed between them.
In the typical manufacturing process for forming a high resolution LCD, the HTPS (high temperature polysilicon) having a high mobility of about 30 to 150 cm2/Vxc2x7sec is used for the material of a channel layer in the TFT. When the polysilicon is used, the TFT is formed to have sufficient speed to be utilized as a driver in the LCD.
However, the polysilicon film is typically formed by a SPC (Solid Phase Crystallization) method that applies heat to an amorphous-silicon film formed on the substrate to induce crystallization or by a low pressure CVD method that directly deposits the polysilicon on the substrate. These film making methods are carried out at a high temperature of 700xc2x0 C. to 900xc2x0 C., so the polysilicon TFT LCD production process is called a high temperature process. In the high temperature process, an expensive substrate such as a heat-resistant quartz plate or the like is required, which leads to a high cost. Additionally, the size of the quartz plate has a limitation, which hinders the LCD from achieving large scale.
An object of the present invention is to provide a method of forming a thin film transistor on a transparent plate.
Another object of the present invention is to provide a method of forming a silicon thin film transistor on a glass plate without a high temperature process.
To achieve these objects, the present invention provides a method of forming a thin film transistor on a transparent plate. A semiconductor layer having an active area is provided. A first ion implantation is performed to form a deeper doped region in the semiconductor layer. A second ion implantation is performed to form a shallower doped region in part of the semiconductor layer. A transistor structure is formed on the semiconductor layer located at the active area. A glass plate is formed on the transistor structure. An annealing process whose temperature is about 200xc2x0 C.xcx9c600xc2x0 C. is performed to peel the silicon layer from the deeper doped region and the shallower doped region, and to form a semiconductor thin film adhered to the transistor structure.
The present invention improves on the prior art in that the silicon layer is peeled from the deeper doped region and the shallower doped region to form the TFT on the glass plate with the annealing process whose temperature is about 200xc2x0 C.xcx9c600xc2x0 C. Thus, the invention can use the cheaper glass plate and use single crystal silicon having a higher mobility (about 500 cm2/Vxc2x7sec) than polysilicon as the channel layer in the TFT, thereby reducing cost, raising performance, and ameliorating the disadvantages of the prior art.